1. Field of the Invention
The present invention relates to a flat panel display, and more particularly, to a liquid crystal display including a touch sensitive touch screen.
2. Description of the Related Art
Just as the demand for flat panel displays has surpassed the demand for cathode ray tube (CRT) displays, the growing demand for thinner and lighter personal computers and television sets increases the need for thinner and lighter display devices.
The flat panel displays include liquid crystal displays (LCD), field emission displays (FED), organic light emitting displays (OLED), and plasma display panels (PDP), among other types.
In general, an active matrix type of flat panel display includes a plurality of pixels arranged in a matrix and displays an image by controlling the light emitting strength of each pixel according to given luminance data. A liquid crystal display includes two display panels one having pixel electrodes and one having a common electrode, and a liquid crystal layer interposed between the two display panels having dielectric anisotropy. In order to display an image, the liquid crystal display applies an electric fields across the liquid crystal layer within each pixel and controls the transmittance of light passing through the liquid crystal layer by controlling the strength of the electric field in each pixel.
FIG. 1 is a block diagram of a liquid crystal display having pixels. FIG. 2 is an equivalent circuit diagram illustrating one pixel of the liquid crystal display of FIG. 1.
As shown in FIG. 1, a liquid crystal display includes a liquid crystal panel assembly 300, gate and data drivers 400 and 500 and a sensing signal processor 700, which are connected to the liquid crystal panel assembly 300, a gray voltage generator 800 connected to the data driver 500, and a signal controller 600 for controlling the elements 300, 400, 500, and 800.
A display operation of a liquid crystal display will now be described. The signal controller 600 receives input image signals R, G, and B and an input control signal for displaying of the input image signals from an external graphics controller (not shown). For example, the signal controller 600 receives a vertical synchronization signal Vsync, a horizontal synchronizing signal Hsync, a main clock signal MCLK, and a data enable signal DE.
The signal controller 600 appropriately processes the input image signals R, G, and B to be suitable for an operating condition, and generates a gate control signal CONT1 and a data control signal CONT2.
The data driver 500 converts a digital image signal DAT for one pixel row PX to an analog data voltage according to the data control signal CONTS from the signal controller 600, and applies the analog data voltage to a corresponding data line D1-Dm.
The gate driver 400 applies a gate-on voltage Von to the gate lines G1-Gn according to a gate control signal CONT1 from the signal controller 600, and turns ON switching elements Q connected to the gate lines G1-Gn. Then, the data voltage applied to the data lines D1-Dm is applied to a corresponding pixel PX through the turned-on switching element Q.
The difference between the data voltage and the common voltage Vcom applied to the pixel PX is shown as a charge voltage of the liquid crystal capacitor Clc (see FIG. 2), a pixel voltage. The arrangement of liquid crystal molecules changes according to the pixel voltage. Accordingly, the polarization of light passing through the liquid crystal layer 3 changes. A polarizer changes the transmittance of light to change the polarization, and the pixel PX displays luminance that represents the gray of an image signal DAT.
By repeating the described operations in units of a 1 horizontal period (or “1H”, which is one period of the horizontal synchronizing signal Hsync and the data enable signal DE], the gate-on voltage Von is sequentially applied to all of the gate lines G1-Gn and the data voltage is applied to all pixels PX, thereby displaying images of one frame.
Referring to FIG. 1, the liquid crystal panel assembly 300 includes a plurality of display signal lines G1-Gn and D1-Dm, a plurality of pixels PX connected to the display signal lines G1-Gn and D1-Dm and arranged like a matrix.
Referring to FIG. 2, the liquid crystal panel assembly 300 includes a thin film transistor array panel 100, a common electrode panel 200 facing the thin film transistor array panel 100, a liquid crystal layer 3 interposed between the two panels 100 and 200, and a spacer (not shown) that is compressible to a predetermined level for maintaining a predetermined distance between the two display panels 100 and 200.
The display signal lines G1-Gn and D1-Dm include a plurality of gate lines G1-Gn for transferring gate signals and a plurality of data lines D1-Dm for transferring data signals.
The gate lines G1-Gn extend basically in a row direction (horizontally) and run almost parallel to each other. The data lines D1-Dm extend basically in a column direction (vertically) and run almost parallel to each other.
As shown in FIG. 2, each pixel PX, for example a pixel PX connected to the ith (i=1, 2, . . . , n) gate line Gi and the jth (j=1, 2, . . . , m) data line Dj, includes a switching element Q connected to the signal lines Gi, and Dj, and a liquid crystal capacitor Clc and a storage capacitor Cst, which are connected to the switching element Q. The storage capacitor Cst may be omitted if unnecessary.
The switching element Q is a three-terminal element such as a thin film transistor (TFT) that is disposed on the thin film transistor array panel 100. The switching element Q includes a control terminal connected to the gate lines G1-Gn, an input terminal connected to the data lines D1-Dm, and an output terminal connected to the liquid crystal capacitor Clc and the storage capacitor Cst. The thin film transistor includes amorphous silicon or polysilicon.
The liquid crystal capacitor Clc uses a pixel electrode 191 of the thin film transistor array panel 100 and a common electrode 270 of the common electrode panel 200 as two terminals. The liquid crystal layer 3 between the two electrodes 191 and 270 functions as a dielectric material. The pixel electrode 191 is connected to the switching element Q. The common electrode 270 is formed on a front surface of the common electrode panel 200 and receives a common voltage Vcom. Alternatively, unlike as shown in FIG. 2, the common electrode 270 may be provided on the thin film transistor array panel 100. At least one of the two electrodes 191 and 270 may be linear or rod shaped.
An additional signal line (not shown) disposed at the thin film transistor array panel 100 and the pixel electrode 191 overlap each other with an insulator interposed therebetween to obtain the storage capacitor Cst in each pixel that supplements the liquid crystal capacitor Clc, and a predetermined voltage such as the common voltage Vcom is applied to the additional signal line. However, the pixel electrode 191 may overlap a previous gate line with the insulator interposed therebetween to obtain the storage capacitor Cst
A touch screen panel is a device, such as a display device, that senses touch, and may be used to control an apparatus such as a computer to perform a desired command. The touch using a finger, a touch pen, or a stylus may be sensed writing text, drawing figures on a screen, or executing a related icon. A liquid crystal display having a touch screen panel can detect whether or not contact is being made on the display by a user using a finger or a touch pen. Also, the liquid crystal display having a touch screen panel can detect the location of the contact and output the location information. The cost of a liquid crystal display, however, increases due to the addition of a touch screen panel. Because of the additional manufacturing process of adhering the touch screen panel to the liquid crystal panel, the yield of a liquid crystal display is reduced, the luminance of the liquid crystal panel is reduced, and the overall thickness of the product increases.
In order to overcome such problems, a technology of embedding sensors in a liquid crystal display, instead of adhering the touch screen panel thereto, has been developed. The sensors determine whether or not contact is being made (e.g., by a user's finger), and detect the contact location by sensing light variation or pressure variation made by the user's finger.
Such sensors are arranged in a row and column direction and output detection signals indicating touch location to an external reader through wires. The reader is typically implemented as an additional IC and connected to the wiring of the display panel through a printed circuit board (PCB).
Typically, the higher the degree of integration a sensor has, the greater the number or wires it has. Therefore, a non-display region occupies a wider area in a display panel. Also, since an integrated circuit (IC) needs the same number of contact bumps (pins) as the number of wires, the size of the IC increases.
Therefore, it is desirable to reduce the number of wires for touch sensors in a liquid crystal display.